Patent GB-1115177-A (GB)
Title: Control device for automatic air brakes
IPC: B60T13/66
Filed: 1965-11-12
Abstract: 1,115,177. Fluid-pressure braking systems. OERLIKON-BUHRLE HOLDING A.G. 12 Nov., 1965 [12 Nov., 1964], No. 48137/65. Heading F2F. In automatic compressed air brakes for railway vehicles, service applications of the brakes due to pressure reduction in the brake pipe 44 caused by actuation of a driver's valve 40 are effected by means of an electrical circuit acting through a braking wire 60 running the entire length of the train, the circuit being influenced by the difference between a pilot pressure in a pipe 46 which can be reduced by the driver's brake valve 40 and the pressure in the brake pipe 44 and responding when the latter pressure exceeds the pilot pressure by more than the certain minimum value. A safety device in the form of a blow-off valve 35 for the brake pipe which initiates emergency application of the brakes when an actuating member opens is provided and the actuating member is responsive to the pressure difference exceeding a certain minimum value between the brake pipe pressure and the pilot pressure existing in the pilot-pressure system. When the blow-off valve 35 is open, a chamber 3 of the blow-off valve connected to the pilot-pressure pipe 46 is connected to atmospheric pressure and the chamber 4 of the blow-off valve connected to the brake pipe 44 is provided with a narrow escape port 12 such that a back pressure is created in the blow-off valve which ensures that the pressure difference required to hold the valve open continues to exist until the brake pipe is completely empty. Both chambers 3 and 4 of the blow-off valve are connected to one another by means of an additional valve 18 which is controlled during release of the brakes by an electrical energizing circuit containing a switch 48 fitted with a clockwork delay mechanism. In operation, service braking is effected by actuation of the driver's brake valve 40 into the braking position such that the pilot pressure is reduced and the pressure in the brake pipe is lowered. The reduction of pressure in the brake pipe is delayed so as to create the difference between the pilot pressure in the pipe 46 and the pressure in the brake pipe 44 which is sufficient to close a switch 47 by means of a braking and release mechanism 50 which responds to a minimum pressure difference. Brake application current then flows through the wires 60, 56 and 62 via energizing coils 38 of braking valve 34 which connect the brake pipe to the outside atmosphere in individual carriages of the train. A triple pressure valve 68 responds to the difference in the pressure between the brake pipe and the constant pressure reservoir 59 and control the flow of compressed air from the auxiliary reservoir 49 to the brake cylinder 69. Should there be a defect in the electrically controlled braking mechanism, the valves 34 are either only partially opened or not at all and the reduction in the brake pipe is delayed with respect to that pilot pressure. This creates the necessary pressure difference on the piston 5 in the blow-off valve 35 to cause the piston to raise the valve disc 15 from its seat so that the pressure in chamber 3 is connected directly to outside atmosphere. Since air at the pilot pressure can only flow through the choke 33 provided in the pilot pressure pipe 46, the pressure in the chamber 3 falls to atmospheric level. Movement of the piston 5 in the blowoff valve 35 continues under the influence of the pressure in the brake pipe 44 to lift the valve disc 9 from its seat and allow air from the chamber 4 to escape to atmosphere via a restricted port 12 to initiate an emergency application of the brakes. When the brake pipe pressure has been exhausted the valve 35 closes again and the pilot pressure now builds up again in the chamber 3. A manual switch 64 is then closed to isolate the blow-off valve 35 and energize the solenoid 27 to close the valve 18 so that the two chambers 3 and 4 of the blowoff valve are connected together to prevent automatic opening of the blow-off valve. To release the brake, the driver's brake valve is moved to its release position which raises the 'pilot pressure and at the same time raises the brake pipe pressure. The rise in the brake pipe pressure is delayed so that a difference exists between the pilot and the brake pipe pressures which causes the braking and release mechanism 50 to close a switch 67 and allow current to -flow through the wires 61, 57 and 62 to actuate solenoids 37 of release valves 31 which connect the brake pipe with the supply pipe 39 in the individual carriages. To prevent charging pulses being generated in the brake pipe 44 when the brakes are released, a switch 48 is held closed by the release current -flowing through its actuating solenoid 32 so that the solenoid 27 is energized and the valve 18 maintain's communication between the chambers 3 and 4 of the blow-off valve 35. When charging is complete and the release current is again switched off, the clockwork delay mechanism of the switch 48 maintains it closed for a short period so that the charging pulses shave time to die away before the switch 48 interrupts the flow of current to the solenoid 27.